§ 3.111 VISCERAL MUSCLE 01 



to the perfusate. Only one of these shows the same action as the 

 crude extract; this active constituent is thought to be an ortho- 

 diphenol (and therefore related to adrenaline). Beautiful as this 

 technique is, it only demonstrates, like most experiments on organ 

 extracts, the pharmacological fact that the animal produces a 

 chemical which has an effect upon the heart. It would be another 

 matter to show conclusively that in life the heart beat is physio- 

 logically controlled in any way by this substance, or that in the 

 absence of the corpora cardiaca the animal is unable to control its 

 heart beat to suit the conditions under which it is living. The 

 stimulus which might cause the secretion of the chemical is 

 unknown. 



The corpus cardiacum acts as a storage organ for a neurosecretion 

 from the brain, as can be seen in Leiicophaea^ where severing the 

 nerve on one side prevents the passage of the secretion (Fig. 3-2). 

 Yet if a similar operation is performed on Periplaneta and separate 

 extracts of the corpora cardiaca of the two sides are tested after 

 5 and 17 days, that from the severed side is still as active as the 

 other. This eliminates the neurosecretion as a source of the heart- 

 accelerating hormone, which must be the intrinsic secretion of 

 the corpus cardiacum itself. These cells are of ectodermal, rather 

 than nervous, origin (§ 2.112), so that their secretion is one of the 

 few kinetic hormones that is not a vascular "neurohormone" 

 (Welsh, 1955), although its action is akin to that of adrenaline, 

 secreted from cells of the vertebrate sympathetic nervous system 

 (Mendes, 1953). 



Adrenaline itself has a similar stimulating effect upon the 

 heartbeat of many invertebrates, whether it is neurogenic or 

 myogenic; but there is as yet no clear evidence of its being 

 secreted by any gland in an invertebrate. In only a few inverte- 

 brates is adrenaline used as a chemical transmitter at any nerve 

 ending. 



Vertebrata. Adrenaline (§2.111) increases the amplitude 



same specimen throughout the series : {A) extract of pericardial 

 organ of Cancer ; {B) adrenaline (1 :10«) ; (C) noradrenaline (1 :10«) ; 

 {D) the same extract as in {A). Between exposures to these sub- 

 stances the heart is restored to seawater and the beat slows down 

 with a reduced amplitude (from Alexandrowicz and Carlisle, 1953). 



